The Mars Exploration Rovers ("Spirit" and "Opportunity") have performed well beyond their expected lifespans, and have by all measures been an enormous success. But they roll slowly around the surface of Mars, and have gone just a few kilometers each, largely avoiding any kind of rough terrain. In order to get a better look at the variety of the Martian landscape, we'll need something which can move faster over any kind of ground. Something which can fly, but which can also land and take samples, repeatedly.
The gashopper would get its electricity from a large set of solar panels built on top of its wings. It would use this electricity to retrieve carbon dioxide from the Martian atmosphere, and then store it as a liquid inside the aircraft. When enough gas was stored up to make a flight, it would heat up a hot bed of pellets and then pass the CO2 through it. Now hot, the gas would act as a propellant, and allow the gashopper to lift off vertically from the surface of Mars. Once airborne, it could then fire more gas out a rear thruster and begin flying as an airplane, using its large wings for lift and maneuverability. When it was ready to land, the aircraft could slow its airspeed, and then touch down gently as a vertical lander.
While still very much in the early-testing/proposal stage, the gashopper has a distinct advantage over many other proposed explorer vehicles: it is designed to use resources already present in the Martian environment (sunlight for power and CO2 for propulsion), so it can keep going as long as the hardware itself is functional. In addition, it won't pollute the Martian atmosphere with chemicals which might confuse any tests for organic material. A sustainable, environmentally-sensitive, wide-ranging exploration system for Mars? I'm all for it.